Chapter 13, Problem 13.33P

Propose a structure consistent with each set of data.

a. a compound that contains a benzene ring and has a molecular ion at $m\text{/}z=107$

b. a hydrocarbon that contains only $s{p}^3$ hybridized carbons and a molecular ion at $m\text{/}z=84$

c. a compound that contains a carbonyl group and gives a molecular ion at $m\text{/}z=114$.

d. a compound that contains $\text{C, H, N and O}$ and has an exact mass for the molecular ion at $101.0841$.

Interpretation Introduction

(a)

Interpretation: The structure of a compound that contains a benzene ring and has a molecular ion at $m\text{/}z=107$ is to be proposed.

Concept introduction: Molecular mass is the sum of the atomic weights of each constituent element multiplied by the number of atoms of that element.

Answer to Problem 13.33P

The structure of the compound that contains a benzene ring and has a molecular ion at $m\text{/}z=107$ is,

Explanation of Solution

The molecular ion peak of a compound is observed at $m\text{/}z=107$.

Possible hydrocarbons are calculated as,

• Divide $107$ by $12$ (mass of one carbon atom). This gives the maximum number of carbon atoms.

$\frac{107}{12}=8$ Carbon atoms (remainder-$11$)

Thus, the possible molecular formula is ${\text{C}}_{\text{8}}{\text{H}}_{\text{11}}$.

The molecular ion has odd mass. Thus, the compound may contain $\text{C, H}$ and $\text{N}$ atoms.

Possible compounds with $\text{C, H}$ and $\text{N}$ is calculated as,

• Substitute $1$ $\text{N}$ for ${\text{CH}}_2$.

${\text{C}}_{\text{8}}{\text{H}}_{\text{11}}\underset{\text{+1 N}}{\overset{-{\text{CH}}_2}{\to }}{\text{C}}_7{\text{H}}_9\text{N}$.

Thus, the possible molecular formula is ${\text{C}}_7{\text{H}}_9\text{N}$.

The molecular mass of ${\text{C}}_7{\text{H}}_9\text{N}$ is $107$. Thus, it will show molecular ion peak at $m\text{/}z=107$.

Hence, the structure of a compound that contains a benzene ring and has a molecular ion at $m\text{/}z=107$ is shown below.

Figure 1

Conclusion

The structure of a compound $\left({\text{C}}_7{\text{H}}_9\text{N}\right)$ that has a molecular ion at $m\text{/}z=107$ is shown in Figure 1.

Interpretation Introduction

(b)

Interpretation: The structure of a hydrocarbon that contains only $s{p}^3$ hybridized carbons and a molecular ion at $m\text{/}z=84$ is to be proposed.

Concept introduction: Molecular mass is the sum of the atomic weights of each constituent element multiplied by the number of atoms of that element.

Answer to Problem 13.33P

The structure of a hydrocarbon $\left({\text{C}}_6{\text{H}}_{12}\right)$ that contains only $s{p}^3$ hybridized carbons and a molecular ion at $m\text{/}z=84$ is,

Explanation of Solution

The molecular ion peak of a compound is observed at $m\text{/}z=84$.

Possible hydrocarbons are calculated as,

• Divide $84$ by $12$ (mass of one carbon atom). This gives the maximum number of carbon atoms.

$\frac{84}{12}=7$ Carbon atoms $\to {\text{C}}_{\text{7}}$

• Replace one carbon by $12$ hydrogen atoms for another possible molecular formula.

${\text{C}}_{\text{7}}\underset{{\text{+12H}}^{\text{'}}\text{s}}{\overset{-\text{1C}}{\to }}{\text{C}}_6{\text{H}}_{12}$

Thus, the possible molecular formula is ${\text{C}}_6{\text{H}}_{12}$.

The molecular mass of ${\text{C}}_6{\text{H}}_{12}$ is $84$. Thus, it will show molecular ion peak at $m\text{/}z=84$.

Hence, the structure of a hydrocarbon that contains only $s{p}^3$ hybridized carbons and a molecular ion at $m\text{/}z=84$ is shown below.

Figure 2

Conclusion

The structure of a hydrocarbon $\left({\text{C}}_6{\text{H}}_{12}\right)$ that contains only $s{p}^3$ hybridized carbons and a molecular ion at $m\text{/}z=84$ is shown in Figure 2.

Interpretation Introduction

(c)

Interpretation: The structure of a compound that contains a carbonyl group and gives a molecular ion at $m\text{/}z=114$ is to be proposed.

Concept introduction: Molecular mass is the sum of the atomic weights of each constituent element multiplied by the number of atoms of that element.

Answer to Problem 13.33P

The structure of a compound $\left({\text{C}}_7{\text{H}}_{14}\text{O}\right)$ that gives a molecular ion at $m\text{/}z=114$ is,

Explanation of Solution

The molecular ion peak of a compound is observed at $m\text{/}z=114$.

Possible hydrocarbons are calculated as,

• Divide $114$ by $12$ (mass of one carbon atom). This gives the maximum number of carbon atoms.

$\frac{114}{12}=9$ Carbon atoms (remainder $=6$)$\to {\text{C}}_9{\text{H}}_6$

• Replace one carbon by $12$ hydrogen atoms for another possible molecular formula.

${\text{C}}_9{\text{H}}_6\underset{{\text{+12H}}^{\text{'}}\text{s}}{\overset{-\text{1C}}{\to }}{\text{C}}_8{\text{H}}_{18}$

The compound that contain $\text{C, H}$ and $\text{O}$ atoms always have a molecular ion with even mass.

Possible compounds with $\text{C, H}$ and $\text{O}$ is calculated as,

• Substitute $1$ $\text{O}$ for ${\text{CH}}_4$.

${\text{C}}_8{\text{H}}_{18}\underset{\text{+1 O}}{\overset{-{\text{CH}}_4}{\to }}{\text{C}}_7{\text{H}}_{14}\text{O}$.

Thus, the possible molecular formula is ${\text{C}}_7{\text{H}}_{14}\text{O}$.

Hence, the structure of a compound that contains a carbonyl group and gives a molecular ion at $m\text{/}z=114$ is shown below.

Figure 3

Conclusion

The structure of a compound $\left({\text{C}}_7{\text{H}}_{14}\text{O}\right)$ that gives a molecular ion at $m\text{/}z=114$ is shown in Figure 3.

Interpretation Introduction

(d)

Interpretation: The structure of a compound that contains $\text{C, H, N and O}$ and has an exact mass for the molecular ion at $101.0841$ is to be proposed.

Concept introduction: Molecular mass is the sum of the atomic weights of each constituent element multiplied by the number of atoms of that element.

Answer to Problem 13.33P

The structure of a compound $\left({\text{C}}_5{\text{H}}_{11}\text{ON}\right)$ that has an exact mass for the molecular ion at $101.0841$ is,

Explanation of Solution

The molecular ion peak of a compound is observed at $m\text{/}z=101$.

Possible hydrocarbons are calculated as,

• Divide $101$ by $12$ (mass of one carbon atom). This gives the maximum number of carbon atoms.

$\frac{101}{12}=8$ Carbon atoms (remainder=$5$ )$\to {\text{C}}_8{\text{H}}_5$

• Replace one carbon by $12$ hydrogen atoms for another possible molecular formula.

${\text{C}}_8{\text{H}}_5\underset{{\text{+12H}}^{\text{'}}\text{s}}{\overset{-\text{1C}}{\to }}{\text{C}}_7{\text{H}}_{17}$

The given compound contains $\text{C, H, N and O}$.

Possible compounds with $\text{C, H, N and O}$ are calculated as,

• Substitute $1$ $\text{O}$ for ${\text{CH}}_{\text{4}}$.

${\text{C}}_7{\text{H}}_{17}\underset{\text{+1 O}}{\overset{-{\text{CH}}_{\text{4}}}{\to }}{\text{C}}_6{\text{H}}_{13}\text{O}$.

• Substitute $1$ $\text{N}$ for ${\text{CH}}_2$.

${\text{C}}_6{\text{H}}_{13}\text{O}\underset{\text{+1 N}}{\overset{-{\text{CH}}_2}{\to }}{\text{C}}_5{\text{H}}_{11}\text{ON}$.

Thus, the possible molecular formula is ${\text{C}}_5{\text{H}}_{11}\text{ON}$ and exact mass of ${\text{C}}_5{\text{H}}_{11}\text{ON}$ is $101.0841$.

Hence, the structure of a compound that contains $\text{C, H, N and O}$ and has an exact mass for the molecular ion at $101.0841$ is shown below.

Figure 4

Conclusion

The structure of a compound $\left({\text{C}}_5{\text{H}}_{11}\text{ON}\right)$ that has an exact mass for the molecular ion at $101.0841$ is shown in Figure 4.